Kishi did not made any error, as he is the story teller.
Only WE, are taking assumption of this Naruto.
In order to understand what Kishi is telling the story, we also need to understand the way he write. Of which many story and/or fiction writer do, certain issue or matter was not told until the it need to be.
"Edo Tensei" vs "Rinne Tensei"
Firstly: These are 2 entirely different meaning of jutsu
"Rinne Tensei" was created by the SO6P as he had it on both eyes.
"Edo Tensei" was created by 2nd Hokage Tobirama. Please take note that this jutsu was finally reveal in the latest chapter where Orochimaru told Tobirama that his jutsu do kill many people.
Second: Rinne Tensei can revived the person and that person's body must be preserve. That could be how Madara had to link.
As for Nagato chakra, any nin just need some time to recover. As Nagato was up to his limit, he revived the Leaf Village people back to Normal Life and he die. Whereas, Tsunade went into coma. Both of their chakra had reached their own limit.
Third: Edo Tensei was revived DEAD person. Think. When a person die, for months and years, their body are just bones.
Now, go back to the current chapter. Orochimaru used 4 bodies, which is zetsu, to become the 4 Hokage. Likewise, whose bodies were Kabuto were using.
This could mean that Kabuto just need any living bodies, and using the soul of the actual person, to make them alive. The bodies were emptiness, as they cannot die. If killed, they re-fix (just like Hidan).
Did you notice that the face of Madara and those 'dead' nin were the same - not smooth. Madara soul...That's why Madara need Obito to be the Jinchuriki of Ten Tails. Like those 6 'dead' Jinchuriki, they are control by Obito....
Fourth: ......
.....to be continue........Thanks for reading..................